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Two Hats for PLC

For signal transduction to occur with rapid temporal resolution (on the order of milliseconds), there must be mechanisms for rapid signal termination (see news and views by Montell). Cook et al. studied phototransduction in Drosophila as one example where the response to the input signal (light intensity and light duration) must be tightly controlled to allow proper temporal and intensity resolution. Phototransduction in Drosophila occurs via activation of a G protein-coupled receptor that activates Gq; that, in turn, stimulates phospholipase C (PLC). The rate-limiting step in signal termination is the rate of GTPase activity of the activated Gq. The authors found that the rate of signal termination and the ability to resolve light of varying intensities were dependent on the concentration of PLC and not on the interaction of PLC with a scaffold protein. PLC acted not only to propagate the light-generated signal, but also to terminate the signal by stimulating the GTPase activity of Gq. These data provide in vivo confirmation of results found in vitro with mammalian PLC: PLC is a GTPase-activating protein (GAP).